How to avoing descent wobble/oscillation???

[PCMAerial]

How to avoid descent wobble/oscillation???

Having some trouble with a new quad oscillating and wobbling pretty heavy on descent. This is while descending straight down, and at an angle while moving. Wondering if anyone has any idea of how to solve. Below is my setup and possible ideas...

-Quadframes Carbon Fiber 770mm
-Tmotor 700kv U3
-12 Inch Cf Props
-30a ESC (SimonK)
-Naza v2
-Zenmuse

The naza is brand new just setup. Everything calibrated, the rig flies smooth in most directions. But when I descend at pretty much any speed I get some crazy wobbles, oscillation, and the copter sometimes will yaw on it's own.

My ideas of the problem:
-Boom arms too long? 770 quad - Thinking of shortening to 600-650. But also need enough room for bigger props
-Boom arms not even? One or two of the booms don't look the same length.
-New props needed - Current props have a few scuffs and minor abrasions (bought used)

Anyone have any possible idea on the situation? I have done research on the whole 'land at an angle, but then the copter yaws to the left and I must correct it. I'm sure something just needs some tweaking but not sure what exactly will cure this issue. Thanks for looking!

 

[Phil550]

On page 6 of the Naza M V2 Quick Start Guide it does say:

'For big aircraft that is larger than 650 or with heavy load, WKM is recommended'

So it could be this....

 

[PCMAerial]

On page 6 of the Naza M V2 Quick Start Guide it does say:

'For big aircraft that is larger than 650 or with heavy load, WKM is recommended'

So it could be this....

Interesting. Definitely makes me want to go ahead and shorten the arms. Right now the only precut cf booms I can make work put it at either a 530mm or 680mm. I know I'll need enough span to fit 12" props for these motors. The payload is relatively light as well.

 

[Ronan]

I have a 800mm hex with Naza M V2, no bad wobble when descending at a slight angle...

 

[Old Man]

PID's likely just a little too high, or descending too slow through the prop wash. If pretty low to the ground you could also be dealing with ground effect. NAZA has worked well for a lot of 800mm+ Cinestar's so the size of yours is not a problem.

 

[min0nim]

I haven't tried it myself yet (I have a similar issue), but I've heard that reducing your Vertical Gain is the way to reduce shake on decent.

 

[PCMAerial]

PID's likely just a little too high, or descending too slow through the prop wash. If pretty low to the ground you could also be dealing with ground effect. NAZA has worked well for a lot of 800mm+ Cinestar's so the size of yours is not a problem.

Which ones too high can have affect on this? I tried to set my gains to default and now they're WAY off

-Yaw feels like I'm fighting it to turn, very hard to yaw
-On yaw I almost feel it about to tip over

Lowering my vertical gain did seem to have a small change on the problem. Although ALL of the other gains were set to default so now there are new problems to tune up.

 

[PCMAerial]

I haven't tried it myself yet (I have a similar issue), but I've heard that reducing your Vertical Gain is the way to reduce shake on decent.

Reducing the vertical gain seemed to make a small difference. Although when I lowered, I reset gains so now they're all out of wack. Less oscillation, now way more struggle to yaw properly. Researching if that means I need to lower or raise my yaw gain

 

[PCMAerial]

Currently tuning..

Got the Roll and Pitch gains all the way down to 80. Seems to fly decent in those aspects. Not much oscillation during descent. Although this seems low compared to other people's settings. And now a whole new bucket of tuning problems..

My yaw is at 200 and it's still acting VERY odd. From yaw at 125 to yaw at 200 things aren't as they should be. The yaw responds very quick, sometimes when I yaw the copter will move upwards about half a foot. The yaw will sometimes snap around quickly and over correct and makes the copter twitch violently. Really a feeling I don't like to see. Working on more tuning in the AM. Anyone have any idea as to the right way to tweak up/down?

I have a hunch that my 700kv U3 Tmotors are asking for more weight, but my copter is only but so heavy. Would this be the reason my roll/pitch need to be as low as 80, and possibly why I have yet to find a proper yaw gain setting??

I also have read that a large quad can have these issues? I'm running a 770mm CF quad. The motors are rated for a quad takeoff weight of 4kg, but I have also read 1.5kg per motor (4). I'm running one 4s lipo, a GoPro and Zenmuse. So the quad is on the light side. REALLY thinking a shortening to 650ish will tone things down a bit. Anyways, thx for looking!

 

[Old Man]

Loose rule of thumb has PID's going lower as the aircraft becomes larger. Another loose concept is P generally runs about 1/2 of I.

Whats the rated max thrust of your motor prop combination at the supplied voltage? About 1/4 of the total combined thrust is what you should be figuring the useful weight at. If you are flying too light your craft can get twitchy but the same occurs when gains are too high, and a 200 value suggests, at least to me, that gains too high are the cause of the problems. As a rule you run the gains up until the craft becomes twitch and dial back until things balance out. That roll and pitch appears to have corrected by reducing the gains may be suggestive of elevated yaw gains. 770 is not too large for your FC by any means.

 

[min0nim]

Interesting. On my Vulcan with the Naza, I have the gains at 200,200,180,180. Sitting about 9kg AGW. I found that at lower settings the bird wasn't very stable. I'm still tuning it, but this was the first pass at controlling all gains with a single remote slider.

PCM, can you post a photo of your setup? I had a real issue when the Naza was too low on my centre of gravity. From that experience, I'd imagine that there would be similar issues if the Naza was mounted too far ABOVE the centre of gravity as well. It may be a positioning thing, and not a tuning thing.

Also - kind of goes without saying - but make sure your Naza is tied down tight. And that you don't have any other cables/etc lose that could be causing vibrations or shifts of mass.

 

[PCMAerial]

Loose rule of thumb has PID's going lower as the aircraft becomes larger. Another loose concept is P generally runs about 1/2 of I.

Whats the rated max thrust of your motor prop combination at the supplied voltage? About 1/4 of the total combined thrust is what you should be figuring the useful weight at. If you are flying too light your craft can get twitchy but the same occurs when gains are too high, and a 200 value suggests, at least to me, that gains too high are the cause of the problems. As a rule you run the gains up until the craft becomes twitch and dial back until things balance out. That roll and pitch appears to have corrected by reducing the gains may be suggestive of elevated yaw gains. 770 is not too large for your FC by any means.

Would the aircraft becoming larger in span, but not weight still apply to this? Most quad's I see are smaller. Not saying it's huge but it just feels a little wide, which also seems to possibly be a cause of this problem. I know the Naza can absolutely handle a craft way bigger than this one. Would shorter booms mean the gains go up?

I just looked up and now see the rated max thrust of each motor is 1000g, now I definitely think that I am underweight. I don't have an option to weigh the copter yet, but with the CF tubes, fairly small RMRC 5100 4s lipo, bit of fpv gear, Zenmuse and GoPro it's a kind of light setup.

I'm going to try and lower the yaw to maybe 100 or 80. I've had trouble from 125-200 on yaw so far so that's not working. I appreciate the advice!!! Thanks alot

 

[PCMAerial]

Interesting. On my Vulcan with the Naza, I have the gains at 200,200,180,180. Sitting about 9kg AGW. I found that at lower settings the bird wasn't very stable. I'm still tuning it, but this was the first pass at controlling all gains with a single remote slider.

PCM, can you post a photo of your setup? I had a real issue when the Naza was too low on my centre of gravity. From that experience, I'd imagine that there would be similar issues if the Naza was mounted too far ABOVE the centre of gravity as well. It may be a positioning thing, and not a tuning thing.

Also - kind of goes without saying - but make sure your Naza is tied down tight. And that you don't have any other cables/etc lose that could be causing vibrations or shifts of mass.

What motors are you running on the vulcan? On my previous hex with stock dji motors my gains were around ~200 for this same GoPro and zenmuse. So it's odd to me to have way lower gains on a quad with the same setup, just bigger motors and way larger diameter.

Below I have pictures of my naza. It is mounted on the middle plate and I have my Zen GCU on the top. Along with the GPS. I have my Naza velcroed down but I'll try some 3M tape instead and see what happens.


My guess is I may be underweight and need a bit smaller frame & prop. Maybe 11" on a 650 frame. These motors seem to be asking for more. Wondering if that's causing this crazy tilting when I yaw

Thanks for the advice!!!!

 

[PCMAerial]

EDIT:

So I did the research wrong. And my motors are rated to 1600g at 100% thrust on my 14.8v battery. That's 14lbs!!!! I'm probably maxing 5-6. Suspecting this may be a slight cause of the problem

 

[SJBrit]

EDIT:

So I did the research wrong. And my motors are rated to 1600g at 100% thrust on my 14.8v battery. That's 14lbs!!!! I'm probably maxing 5-6. Suspecting this may be a slight cause of the problem

Yeah, that's seems light for that much thrust. The rule of thumb I hear from reputable sources is no less than 30% throttle at hover. Maybe someone with direct experience can confirm that.

 

[PCMAerial]

So now I'm at a crossroads. IF my quad being too light is causing this erratic behavior, what can I do to fix the problem. I see that an 11 inch prop will generate less thrust, so that is number one.

I guess if anything it's easier to add weight than to lose it. But right now I'm about maxed out on things to add. Hmmm

 

[maxwelltub]

Just add a bigger battery. If you need to add weight make it juice

 

[SJBrit]

You could add some weight just to see if that really is the issue. If it is then you're better off reducing thrust than carrying ballast.

 

[Old Man]

I fat fingered 1/4. It was supposed to have been 1/2. Weight is indeed the controlling factor for lift- thrust but size in various areas influences control response, largely via propeller size and motor/ ESC through propeller response.


Sent from my iPhone using Tapatalk

 

[PCMAerial]

I fat fingered 1/4. It was supposed to have been 1/2. Weight is indeed the controlling factor for lift- thrust but size in various areas influences control response, largely via propeller size and motor/ ESC through propeller response.


Sent from my iPhone using Tapatalk

Thank you all for the information! I'm wondering if weight controls the crazy pitch that happens when I yaw. My rig looks like it wants to flip but snaps back level

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I'm going to try this:
-Shorter arms (650mm motor to motor vs 770mm)
-Reduce prop size (Currently 12" to 11" carbon fiber)
-Add battery weight..somehow.

Currently I have a 5100mah 4s. Around 550g. I don't know if I should run this in parallel with another 5100. Or purchase a 8800 which is 900g. A little more weight but honestly not much. I also added a lipo to run my FPV but it's only 250g so not much help. The thrust is a bit lower on spec charts with 11" prop so I will def be trying to "reduce" the size of this all around, and then try to get way more battery since I can allow the extra weight. The guys above are correct, if I need more weight make it in battery power
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